Straws that break the camel's back - like the June 1914 assassination of Franz Ferdinand in Sarajevo. Apparently trivial actions, which unlock mighty forces previously cloaked behind an apparently-manageable surface normalcy.
Cyprus, or something like it, could be the spark. The populations of the 'Club Med' countries are increasingly tired of endless, depressing gloom and resentful of the (perceived) 'so-superior' Germans.
When enough of them feel they have suffered enough, watch out!
